Question: Solve for $q$ : $6 = 13 + q$
Solution: Subtract $13$ from both sides: $ \begin{eqnarray} \\ \hphantom{6 {- 13}} &\hphantom{=}& \hphantom{q} \\ 6 &=& 13 + q \\ \\ {-13} && {-13} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 6 {- 13} &=& q \\ \end{eqnarray} $ Simplify. $ q = -7$